In the past, a control system of an internal combustion engine which is provided with an air-fuel ratio sensor in an exhaust passage of the internal combustion engine and controls the amount of fuel supplied to the internal combustion engine based on the output of this air-fuel ratio sensor, has been widely known. In particular, as such a control system, one which is provided with an air-fuel ratio sensor at an upstream side of an exhaust purification catalyst provided in the engine exhaust passage and which is provided with an oxygen sensor at a downstream side thereof, is known (for example, PLT's 1 to 4).
In particular, in the control system described in PLT 1, the amount of fuel fed to the internal combustion engine is controlled in accordance with the air-fuel ratio detected by the upstream side air-fuel ratio sensor so that this air-fuel ratio becomes a target air-fuel ratio. In addition, the target air-fuel ratio is corrected in accordance with the oxygen concentration detected by the downstream side oxygen sensor. According to PLT 1, due to this, even if the upstream side air-fuel ratio sensor deteriorates due to age or there are individual variability, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst can match with the target value.